Low-resistance connector



July 5, 1966 w. A. CASLER 3,259,727

LOW-RESISTANCE CONNECTOR Filed Oct. 16. 1963 3 s s 1 23 FIG- /C'IG'8 L[i /7 if 7 9 /9 H a INVENTOR. W/u/AM ,4. (451.5?

July 5, 1966 w. A, CASLER 3,259,727

LOW-RESISTANCE CONNECTOR Filed Oct. 16. 1965 2 Sheets-Sheet 2 53 I FIG.3

INVENTOR.

WILLIAM A. CASLER BY 6! a F IG. H

ATTORNEYS United States Patent 3,259,727 LOW-RESISTANCE CONNECTORWilliam A. Casler, 3487 Barhite, Pasadena, Calif. Filed Oct. 16, 1963,Ser. No. 317,110 11 Claims. (Cl. 200-155) This is a continuation-in-partof my application for Low Resistance Connector, Serial No. 98,443, nowabandoned, filed March 27, 1961, which was a continuation of myapplication for Low-Resistance Rotary Contact, Serial No. 670,470, nowabandoned, filed on July 8, 1957.

This invention relates to electrical contacts, and more particularly tolow-resistance contacts for maintaining or breaking low amplitudecircuits.

In circuits where both current and voltage values are relatively low,even small-changes in contact resistance cause noise that obscures if itdoes not totally mask the low amplitude signals. As a result, the needfor lowresistance contacts exists in many types of service. Principalapplications, however, are to close circuits between non-rotating partsor to at least periodically connect rotating parts. Virtually everycircuit breaker illustrates the former application. Many examples of thelatter are also at hand. For example, to carry indications from straingauges or other sensing equipment mounted on rotating parts to auxiliaryinstrumentation where such signals are interpreted, to carry errorsignals for the control of servo motors, and to carry signals fromrotary position indicators, navigational instruments or radio signals toor from rotating antennas where high fidelity of reproduction must becontinued during rotation of the equipment. For any of the servicesmentioned and for many others, either the effective impedance of theapparatus supplying the signals may be very low, of the order of perhaps2 or 3 ohms, or the changes in impedance which effectively generate thesignal currents may be of this order. In these and other cases, minutevariations in resistance at points of electro-mechanical contact canintroduce errors which greatly reduce the performance of a system.Furthermore, metal oxides, minute contaminants, vibration, wear, andother deleterious factors can, in some applications, so greatly increaseresistance between contacting surfaces that operating life andreliability are significantly reduced.

The principal purpose of the present invention is to provide electricalcontacts for connecting and/or controlling electrical circuits,particularly where small voltage or current signals or other factors (asdiscussed above) make it desirable or mandatory to provide low, constantresistance circuit paths through circuit controllers. This purpose isaccomplished in the instant case by a construction which provides wipingaction between the contacting surfaces as they engage and thereaftermaintains a plurality of high unit pressure contact points between thecontacting parts. For purposes of clarity the invention may beconsidered in the environment of rotating contactors and switches andconventional multi-pole (stationary) switches. The problems are to someextent different but the broad concept of utilizing high unit pressurecontact points and wiping the contacting surfaces is common to both.These construction features more particularly includes a flexibletransfer contactor that mechanically and electrically engages one ormore contactor elements along extended lengths of groove or wedgeseating surfaces formed therein thereby to provide the desired wipingaction and high unit pressure contact points.

This broad purpose may be first discussed in connection with rotarycontacts requiring minimum variation in contact resistance andconsequent noise generation during rotation of the parts between whichcontact must be established. Objects are to provide a rotary contacting3,259,727 Patented July 5, 1966 means wherein the unit pressure betweenthe contacting parts can be made very high and the contact resistancecorrespondingly low and invarient; to provide such means forestablishing high uni-t pressure which are nonetheless of themselveslight, compact, and easy to handle; to provide contacting means where amajor portion of the current transferred between the rotating andstationary parts is carried between contact elements that are themselvesstationary relative to each other but wherein a wiping action, tendingto clean the contacting surfaces, nonetheless takes place constantly ascontact is established and broken between successive relatively minuteareas of the parts in contact; to provide a contacting device which isequally applicable to high or low rotational speeds, and to conditionswhere the rotation is either continuous or intermittent; and to providea device composed of light and easily fabricated parts and which issimply and easily assembled or disassembled.

In addition to these objects that relate primarily to the electricalaspects, objects relating to mechanical features are to provide acontact that is simple to fabricate, is insensitive to misalinement,vibration and dirt and is low in cost.

Considered broadly, the rotating contact embodiment of the presentinvention comprises a circular contact member mounted on the inner oneof two relatively rotatable parts (for convenience hereinafter referredto as the rotor) this member having a generally V-shaped groove formedin its outer periphery. Surrounding the inner contact member is acontact ring mounted on the outer member (hereinafter referred to as thestator), this ring being substantially concentric with the inner memberand also having a generally V-shaped groove formed in its innerperiphery. It is to be understood that the distinction between rotor andstator is purely arbitrary; the rotor may actually be the stationarymember about which the stator rotates.

I Held between the circular contact and the ring is a transfer contactor armature which, when not so held and there distorted, is a spring oftoroidal form whose diameter is greater than the radial separationbetween the grooves in the rotor and stator contacts. For mostapplications this spring or transfer contact is preferably in the formof an electrically continuous, helically wound spring, although for somepurposes it may be one or more circular loops of spring material. Owingto its diameter, when it is sprung into place to engage the grooves inboth rotor and stator contacts, it is distorted into a generallykidneyshaped form that contacts a material are within the groove of boththe rotor and stator contacts. The inherent resilience of this springcontact wedges it into the V-shaped grooves so that the unit pressurebetween the sides of the grooves and the lines of contact formed betweenthe sides of the grooves and the spring can be greatly in excess of thediametric force exerted by the spring in its tendency to assume itsnatural form as a circular toroid. The excess in diameter of theundistorted spring over the separation between the rotor and statorcontacts also insures that a material are of both the rotor and statorcontacts is in contact with the spring. When rotation occurs the springrolls around the periphery of both contacts at a rate dependent upon therelative diameters of the rotor and stator contacts and no slippageoccurs between the two arcs of contact. At each end of these arcs,however, where the spring is entering and leaving the respective groovesas it rolls, a minute wiping action occurs. This wiping action underhigh unit pressure tends to keep the lines of contact clean, removingdust particles and penetrating oxidation so that by the time any portionof the spring has entered the arc of contact with either of the twogrooves the parts are in firm and low-resistance engagement, with manypaths in parallel between the contacting parts.

Nearly all metals exposed to the atmosphere acquire at least a minutefilm of oxide. All materials are subject to contamination by oil, dustand other foreign substances. The high unit pressure as the coils turnto enter the grooves causes them to cut through and wipe off any ofthese contaminants, and as the coils wedge into the grooves themetal-to-metal contact is maintained during the period throughout whichthe coils are stationary relative to the grooves. There are thus manyparallel, lowresistance paths between the relatively rotating parts. Itis only the entering and leaving turns that are changing in resistancein opposite senses and are but a small proportion of the totalconductance.

Moreover, because of the flexibility of the contacting loop, mutualvibrational movement between the rotating parts is absorbed and does notdisturb the 'wedged-in contacts, so that the circuits in which thecontacts are employed is free of microphonic interference from suchvibration. Similarly, the flexibility of the spring loop makes thedevice substantially shockproof.

Turning next to a consideration of the less demanding stationary switchembodiment, it comprises a pair of parallel disposed contacts and aresilient transfer contact or armature biased to jam partially betweenfacing surfaces of the contacts and along a substantial length thereof.This provides a low resistance path between the contacts (by virtue ofthe high unit pressures developed at the multiple points of contact)which follows the scraping action as the armature snaps into contactingposition.

In the illustrative embodiment disclosed, the parallel contacts are apair of flat strips disposed in planes that intersect at an acute angleoutwardly from the location of the transfer contact; the V-shaped grooveso formed is quite similar to those formed in the rotor and stator ofthe other embodiment. Cooperating with these circuit terminals is thetransfer contact in the form of a section of a helically wound springthat is compressed end to end and operated by a toggle that snaps it offcenter to a position bridging the contacts or to an open part of theswitch body. The inherent resilience of the spring contact wedges it inthe V-shaped groove. The unit pressure, here too, is high which assuresa low resistance path for signals transmitted thereover. The length ofcontact between the transfer contact and strips may be controlled by therelative location of the parts and by using arcuate shaped contactstrips. In all cases, as the helical spring wedges between the fixedcontacts, it scrapes the surfaces thereby removing oxidized particles,dust or other foreign materials that cause variable and/or high contactresistances.

The preferred forms of the invention, together with severalmodifications applicable to various somewhat different services willnext be described. In the drawings, illustrative of these descriptions:

FIG. 1 is an axial sectional view illustrating the rotating contactembodiment of the invention as applied to a double contact for carryingboth sides of an instrumentation circuit such as that including a straingauge;

FIG. 2 is a plan view of the apparatus shown in FIG. 1, partly insection, illustrating more clearly the kidneyshaped contour taken by thespring transfer-contact when in place;

FIG. 3 is a partial plan view taken along line XX of FIG. 1 toillustrate one embodiment in which the rotor and stator might besegmented to complete circuit paths other than as illustrated in FIG. 2;

FIG. 4 is a partial plan view taken along line XX of FIG. 1 toillustrate another embodimentin which the rotor and stator might besegmented to complete circuit paths other than as illustrated in FIGS. 2and 3;

FIG. 5 is a fragmentary drawing illustrating a helicalspring type oftransfer contact and indicating one method of forming continuous helicalsprings for the rotating contact embodiment;

FIG. 6 is an isometric View showing the manner of bending the ends ofthe wire forming a helical spring preparatory to joining them to form atoroid;

FIG. 7 is a view similar to FIG. 6 showing the wires connected;

FIG. 8 is a radial cross-section view through one of V-groovedcontacting members of the rotating contact embodiment showing a numberof generally rectangularshaped leaf springs in contact therewith;

FIG. 9 is a similar view showing a helical toroidal spring in engagementwith a slightly different, contoured form of a V-groove utilized in therolling contact embodiment;

FIG. 10 is a side sectional view illustrating the stationary switchembodiment of the invention as applied to a two-pole switch for openingor closing an electrical path; and

FIG. 11 is an end cross section taken along line 1111 of FIG. 10.

FIG. 1 of the drawing shows a small portion of the frame .1 of thestator of a device wherein it is desired that both sides of a circuit becarried to the rotor. The portion shown of the frame 1 carries a bearing3 in which the rotor-shaft 5 turns. An insulating sleeve 7 is forced,keyed or otherwise secured on the shaft and a pair of circular contacts9 are securely fixed to this sleeve. Conveniently the sleeve 7 may be ofan insulating plastic, preferably one of the thermo-setting plasticssuch as Bakelite or other phenolic, and the contacts 9 may be moldedinto the sleeve, forming a single integral unit. In the outer peripheryof each of the contacts there is for-med a V-shaped groove 11.

An insulating cylinder 13 is secured to the frame 1, for example, byscrews 15, so that its inner periphery is concentric with the shaft 5and circular contacts 9. Like the sleeve 7, the cylinder 13 may also beformed of one of the plastics. The sleeve carries a pair of contactrings 17, each of which has a V-shaped groove 19, similar in shape tothe grooves 1 1, formed in its inner periphery, Each of the grooves 19is substantially coplanar with a corresponding groove 11.

The elements 9 and 17 are preferably formed of one of the goodconductors, such as brass, copper or silver, which are fairly resistantto corrosion, so that contact resistance to it is low. For the type ofservice wherein the present invention is likely to be used gold wouldWork; coin silver is one of the best materials because of its resistanceto both corrosion and wear, but the other materials mentioned are verynearly as satisfactory. For light duty silver-plated bronze. or copperis satisfactory but for high-speed rotating machinery solid metal ispreferred because even though the wear is slight, with continuousrotation a thin plating will soon wear through since plated coatings areordinarily soft. On the other hand, high speed operation and the wearresulting from it tend to keep contacting surfaces clean. For suchpurposes beryllium-copper is preferred, but the other materialsmentioned are quite satisfactory.

Leads 21 and 21' are schematically shown as connected to the circularcontacts 9 and leads23 and 23' are similarly shown as connected to thecontact rings 17. These leads represent the two sides of the circuitthrough which contact is to be established. Contact between leads 21 and23 and 21 and 23' respectively is made through intermediate springcontacts 25. FIGS. 3 and 4 show alternative Ways in which circuits mightbe completed.

For example, it might be desirable to complete a path.

between two segments of the stator (01' rotor). In this case, aninsulating separator 51 may form segments 52-54 on the stator 17. Anytwo of these will be bridged by contact 25 as it revolves (FIG. 3).Another circuit arrangement is provided by segmenting the stator intosmall conducting sections 5557 as illustrated in FIG. 4.

In the latter, the transfer contact 25 will commutate a signal at therotor 9 sequentially to segments 55, 56 and 57 of the stator 17.Numerous variants may be perceived inasmuch as the location of thecontacts isnot critical, only the use of the wedging action alongextended portions of the contacts through which the low resistancecircuit must be established. This being the case, whenever the claimsrefer to contacts between the rotor and stator, it is intended that theyinclude circuits established between segments on the rotor or stator aswell as commutating arrangements. Additionally, the sides of the statorforming the V-shaped groove may be insulated to form circuit terminalsthrough which a path is closed by the transfer contact or armature.

A preferred form of the intermediate or transfer contacts is bestillustrated in FIGS. 2-5. FIGS. 2-4 show the form assumedby them when inplace as shown in FIG. 1 while FIG. 5 shows such a contact inundistorted form, prior to being snapped into place. Each of thecontacts 25 is in the form of a continuous loop or toroid of springmaterial. The preferred form, shown in FIG. 5, is a helically woundspring of highly resilient wire, such as beryllium-copper, with its endsbrought together so that electrically and mechanically the spring formsa continuously toroidal helix. It is important that the joint, shown inFIG. 5 at 26, should not materially aifect the flexibility of the springor weaken it, at the point where it is formed. It has been found thatthis can be accomplished by bending the end of the wire, of which thehelix is formed, at right angles so that it projects radially inwardtoward the center of the toroid at both ends of the spring. The twoinwardly projecting ends are abutted and connection between them is madein any suitable fashion, as by twisting, welding or soldering, orpreferably by both twisting and welding or soldering. The projectingends might also be fastened inside the helical windings in cases wheresuch construction might be superior to the projecting joint illustrated.

The diameter of the toroid 25 must exceed the separation between thegrooves 11 and 19, and preferably it is much greater than theirseparation; it may be equal to or greater than the diameter of thegrooves in the contact ring 17, the upper limit being that when thetoroid is distorted and snapped into place as shown in FIG. 2, the twoends of the loop formed by it do not come into contact, although theymay nearly surround the inner contact 9. In general it is desirable thata large number of turns of the toroid come into contact with each of thegrooves, so that a fairly large diameter is indicated but too large adiameter will sometimes cause the loop to pull away from the centralportion of its contact with the inner groove 11. The preferred diameteris such that when in place the spring is distorted from its originallytoroidal form into the somewhat kidney-shaped form shown in FIG. 2. Hereand in the claims that follow, however, kidney-shaped is intended to beconstrued broadly to include cases where the spring nearly surrounds theinner contact.

The winding of the helical spring must be sufficiently open so thatwhere it is bent most sharply, which may either be around the innercontacts 9 or at the ends of the loops where it is inflected between theinner and outer contacts, the adjacent turns do not quite come intoactual abutment, since such abutment sets a limit to the flexibility ofa spring of the character described.

When the spring is distorted as shown in FIG. 2, its natural tendencyis, of course, to straighten out, thus exerting a radial pressuretending to force it into the V-shaped grooves between which it is held.As the rotor turns it carries the spring with it, and as a result thespring rolls around the inner periphery of the stator contact so thatadditional turns of the spring are continually entering the groove 19and continually advancing point 27 at the advancing end of the loop andleaving the groove 19 at the corresponding point 29 at the trailing end.Similarly new turns are entering the grooves 11 at the point 31 andleaving at the point 33. It is at these points that the spring is moststrongly flexed and the pressure is greatest. The actual contactpressure is materially greater than the radial force exerted by thespring in its attempt to straighten at its point of entry and leavingthe grooves because of the mechanical advantage given by the wedgingaction. The more acute the angle of the V the greater the mechanicaladvantage and the higher the contact pressure, so that even though theradial pressure may be relatively light the contacting pressure isseveral times as great.

As the turns of the spring enter and leave the grooves their planes arechanging. Between the points of entering and leaving the grooves, wherethe turns are in stationary contact with the elements 9 and 17respectively, the planes of these individual turns are very nearlyradial with respect to the device as a whole. At the two ends of theloop the planes of the individual turns are substantially at rightangles to the radius. As the turns enter and leave the grooves theplanes of the turns are changing and as a result there is added to thewedging action a turning or rubbing action which cleans the contactingsurface and gives the advantages of a wiping contact. This actionconstantly takes place as the spring rolls around both inner and outerelements; it speeds the drop in resistance with the individual turns ascontact takes place with each successive turn. As the turns of thespring wedge into the grooves at the advancing of the loop theircircular form is itself slightly distorted so that they :make a shortline-contact with each side of the groove instead of the theoreticalpoint contact, and this also serves to decrease the contact resistance.

If the angle at the apex of the groove is acute and the sidescorrespondingly steep, so that the mechanical advantage is great and thecontact pressure high, the wellknown irreversible property of a wedgecomes into play and the turns remain firmly seated throughout the arcsaround the inner and outer grooves where they are relatively at rest,the contact pressure being exerted by the turns themselves in theirefforts to resume their truly circular form. There is therefore nomeasurable change in the contact resistance throughout the portion oftheir paths where they are relatively stationary with respect to theinner and outer grooves.

There are, of course, numerous modifications that are possible in theconstruction of the various parts of the device. For example, the sidesof the grooves in either or both of the contacts 9 and 17 can becontoured, somewhat as shown through the section 17 of a contact ringillustrated in FIG. 9. Such contouring increases slightly the area ofcontact at the expense of contact pressure. The apex of the groove neednot be carried to a sharp point. It may be rounded as shown in this samefigure, as long as the groove is carried deep enough and the radius atthe apex is enough smaller than that of the helical turns so thatcontact takes place at the sides and not at the bottom of the groove.

It is also possible to use a toroidal spring formed of a single endlesswire loop or a number of leaf springs. The springs need not be ofcircular cross-section; they may be elliptical or substantiallyrectangular in cross-section as indicated at 25' of FIG. 8, wherein thegroove 19" is also shown with a rounded apex. If the loop is a solidwire or a group of leaf springs of non-circular cross-section it shouldbe sufliciently thick, measured radially of the toroid, to be resistantenough to torsion so that, in the case of a loop of rectangularcross-section it will not tend to twist and make a flat contact againstthe sides of the groove, thus defeating the wedging action upon whichmuch of effectiveness of the device depends. Coiled-spring toroids withnon-circular turns can be formed and used but they are diflicult to makeand unless they are carefully designed do not have sufficient torsionalrigidity to be as satisfactory as helically-wound springs with circularturns.

If solid wire loops are used, of either circular or noncircularcross-section, the action that takes place at the point of make or breakdiffers onlyin degrees from that V which occurs to a helically woundloop. In the case of a solid, single-turn spring, each differentiallength around its periphery acts like a turn of a helical spring andforms a rubbing or sliding contact as it enters or leaves the groove.The individual turns or elements of such a solid spring are not asreadily deformable as are those of a helix and the contact area,measured circumferentially around each individual turn iscorrespondingly less. On the other hand the elementary turns are closertogether, so that the over-all area may be just as great. It is a matterof individual choice, depending upon the service to which the individualdevice is adapted, which form of loop will be used. One factor in makingthe choice may be the frequency of currents carried by the contacts; forvery high frequencies the additional inductance of a coil may make asolid-section toroid preferable.

The relative radii of the inner and outer contacts, 11 and 19respectively, are unimportant, the criteria for satisfactory operationof the invention being that the loopdiameter of the'transfer contact begreater than the separation of the grooves and that this separation beconstant throughout the extent of the grooves. It follows that theinvention may be used to connect reciprocating parts, for example, whichmove in parallel paths, since such paths form the limiting case ofcircles of infinite radius. In this case either contact can beconsidered the centra one.

It is recognized that rolling spring-contacts are not new per se. Forexample, Patent No. 2,467,758, issued to N. E. Lindenblad, disclosesfiat circular spring contacts that roll around an innercylindrical'surface to make bridging contacts between adjacentconducting sectors. Devices of this character are intended to carry highcurrents and high voltages and large contact areas are necessary for thepurpose. While satisfactory for use in highcurrent circuits they are notadapted for use in low-current low-voltage circuits such as those towhich the present invention is primarily directed. For one thing, fiatsprings rolling on cylindrical surfaces exert no wiping action. Insteadof dust particles, oxide, or the like being scraped off as the advancingedge of the loop engages, the flat contact springs merely roll up andover such particles. High voltages and high currents will burn away theintercontact material so that it is usually of no moment; lowvoltagecircuits, carrying small current do not have this effect. Another reasonwhy such rolling contacts. are not good low current transfer devices isthat they are incapable of developing the high unit pressures required.

Additionally, experiment has proved that a rolling contact between flatsurfaces, while it gives large contact area, is noisier than is aconventional brush-and-slip-ring engagement. The present invention isobviously not intended to carry heavy power but in the service for whichit is designed it may reduce interferent noise generated by the contactsby as much as 20 db, in comparison with conventional brushes andslip-rings.

The stationary switch embodiment can take many forms, one of which isillustrated in FIGS. 10 and 11. The switch includes a pair of contacts61 and 62 supported along one side of an insulated body member 63. Thetransfer contact 64 is a section of a helical spring supported at oneend 66 at the end of the body member 63 and attached at its other end toa toggle or actuation lever or device 67. The lever 67 is pivotallysupported by pin 66 to the body member 63 and the transfer contact 64 isaxially compressed when disposed along a line between its two points ofrestraint. As a result, as the toggle 67 is moved away from the side ofbody member 63 to which contact strips 61 and 62 are afiixed, thehelical spring 64 snaps into the V-shaped groove formed by the strips 61and 62 (see FIG. 10). In closing a path between contacts 61 and 62, thehelices scrape the sides of the contact strips thereby assuring clean,low resistance contacts. The degree of compressing normally carried bythe transfer contact 64 along with the angle of the V-groove and itsdepth permits the area of contact to be controlled. As noted above, thestrips 61 and 62 can be arcs of circles to increase the area of contact,hence the number of high unit pressure points. When the path through thecontacts is to be interrupted, the toggle 67 is moved the opposite wayto cause the spring 64 to snap to the blank or open side of the bodymember 63. As is the case with the rotary contact embodiment, ratherthan completing a circuit between parallel strips 61 and 62, the circuitpath may be completed between the transfer contact 63 and one or both ofthe strips 61, 62.

It should be apparent that a number of different actuating means canaccomplish the same salutory result. For example, a slide lever or pushbutton can push the compressed helix over the center point. All have incommon that they cause the transfer contact to wedge between the contactstrips. Another variation may be the shaping of the contact elements 61and 62. While illustrated as fiat strips, they can be wires or the like.Similarly, the transfer contact 64 can be varied as suggested inconnection with the rotary transfer contact described above.

Yet other variations should be apparent. The exemplary embodiment ofFIGS. 10 and 11 is for a single throw, single pole switch, whereas theprinciple is equally applicable to more versatile switches. For example,parallel contact strips might be aflixed in each quadrant of a switchbody so that a circuit can be closed between any one of four pairs ofconnectors. Yet another example is a switch wherein one toggle willclose a number of parallel circuits. The variants mentioned here are notinclusive but designed to illustrate the wide application of theinventive concept forming the nexus of the present invention.

Besides those shown and mentioned, other modifications embodying theprinciple of wedging contact and wiping engagement upon which thepresent invention depends are possible. Those illustrated are thereforenot intended as limiting the scope of the invention, all intendedlimitations being specifically set forth in the accompanying claims.

What is claimed is:

1. Means for establishing a low resistance electrical connection betweenmutually rotatable parts comprising an outer contact ring having agenerally V-shaped groove formed in the inner periphery thereof, acircular contact member mounted substantially coaxially within saidcontact ring for rotation relative thereto and having a generallyV-shaped groove formed in its outer periphery substantially coplanarwith and facing the groove in said contact ring, and an endless loopintermediate transfer contact including a spring of generally toroidalform distorted into a generally kidney shaped form and wedged betweenthe V-shaped grooves facing each other, the cross section of the springbeing less than the radial separation between said ring and saidcircular member and the diameter of the undistorted loop being greaterthan the radial separation between said ring and said circular member sothat when so distorted there is an appreciable arc of contact betweensaid spring and each of said ring and said circular contact member.

2. Apparatus as defined in claim 1 wherein said transfer contactcomprises an endless multi-turn helically wound spring.

3. Apparatus as defined in claim 1 wherein said transfer contactcomprises a single endless loop of spring wire.

4. Means for forming electrical contact between mutually movable partscomprising a pair of contact members mounted in substantially coplanarrelationship on said parts respectively, each of said contact membershaving a V-shaped groove formed therein so that said grooves face eachother and are spaced by a substantially constant distance throughouttheir extent, and a transfer contact comprising a continuous springforming a loop the diameter of which when undistorted is greater thanthe spacing between said grooves and a cross section of which is lessthan the spacing between said grooves, said spring being distorted intoa generally kidney-shaped form and wedged into each of the facinggrooves.

5. The invention as defined in claim 4 wherein said spring is ahelically-wound toroid.

6. Means for completing a low resistance path between terminalscomprising, in combination, at least one contact member having sectionsforming a generally V-shaped groove having an acute angle, a transferarmature adapted to cooperate with said contact member, terminalsassociated with selected ones of said sections and said armature, andmeans for moving the armature from a first position out of contact withat least a portion of said contact member to a second position incontact with said portion of said contact member operable to close apath between at least a pair of said terminals by wedging the armaturebetween the sections forming the contact member, said armature inengaging the contact member wiping the contacting surfaces andestablishing a plurality of high pressure points of contact alongextended parts of said armature and said contact members, said transferarmature being a multi-turn, helical wound spring, the planes of theturns of said spring changing with respect to the contacting surfaceupon engagement and disengagement and the compressive biasing of saidhelical spring in part urging the armature to wedge between the sectionsdefining said V-shaped groove.

7. Means for completing a low resistance path between contact memberscomprising, in combination, at least one pair of fixed contact membersforming a generally V-shaped groove therebetween and forming an acuteangle, a resilient movable contact flexibly supported adjacent theopening of said V-shaped groove, means biasing said movable contact tourge it to equilibrium positions outwardly from an imaginary axisthrough its point of support, the movable contact in one of saidequilibrium positionsbeing wedged between the sides of said V-shapedgroove to complete a path between at least a pair of said contactmembers and in another one of the equilibrium positions being out ofcontact with said fixed contact members, said movable contact in wedgingbetween said fixed contact members wiping the contacting surfaces and1t) establishing a plurality of areas of high pressure contact alongextended portions of the contact members, and means operable toselectively direct said movable contact to open and closed pathequilibrium positions.

8. A switch for completing a low resistance path between a pair ofterminals comprising, in combination, a switch body, at least one pairof contact strips supported in said body in spaced apart relation toform a generally V-shaped groove therebetween and forming an acuteangle, a resilient transfer armature attached to the body adjacent eachset of ends of the fixed contact strips for movement between a closedposition in wedged contacting relation with and interior of said grooveand an open position out of contact therewith, said armature in wedgingbetween the strips wiping the contacting surfaces and creating aplurality of high pressure contacting points along extended parts ofsaid armature and said contact strips, terminals associated with saidstrips and said armature to permit at least one path to be closed whenthe armature is in said closed position, means biasing said armaturetowards one of said open and closed positions, and means to selectivelycontrol the movement of said armature to the open and closed positions.

9. A switch for completing a low resistance path between a pair ofterminals in accordance with claim 8 wherein said transfer armature is amulti-turned, helically wound spring biased to assure one of said openand closed positions.

10. A switch for completing a low resistance path between a pair ofterminals in accordance with claim 8 wherein the attachment points forsaid armature lie in a line substantially parallel to the ends of saidfixed contact strips, said transfer armature is a multi-turned helicallywound spring, and the armature is biased toward the open or closedposition by compressing the helix between the points of attachment.

11. A switch for completing a low resistance path between a pair ofterminals in accordance with claim 10 and including a lever pivotallysupported on the switch body to initiate and control movement of thetransfer armature between the open and closed positions.

No references cited.

KATHLEEN H. CLAFFY, Primary Examiner.

J. R. SCOTT, Assistant Examiner.

1. MEANS FOR ESTABLISHING A LOW RESISTANCE ELECTRICAL CONNECTION BETWEEN MUTUALLY ROTATBLE PARTS COMPRISING AN OUTER CONTACT RING HAVING A GENERALLY V-SHAPED GROOVE FORMED IN THE INNER PERIPHERY THEREOF, A CIRCULAR CONTACT MEMBER MOUNTED SUBSTANTIALLY COAXIALLY WITHIN SAID CONTACT RING FOR ROTATION RELATIVE THERETO AND HAVING A GENERALLY V-SHAPED GROOVE FORMED IN ITS OUTER PERIPHERY SUBSTANTIALLY COPLANAR WITH A FACING THE GROOVE IN SAID CONTACT RING, AND AN ENDLESS LOOP INTERMEDIATE TRANSFER CONTACT INCLUDING A SPRING OF GENERALLY TOROIDAL FORM DISTORTED INTO A GENERALLY KIDNEY SHAPED FORM AND WEDGED BETWEEN THE V-SHAPED GROOVES FACING EACH OTHER, THE CROSS SECTION OF THE SPRING BEING LESS THAN THE RADIAL SEPARATION BETWEEN SAID RING AND SAID CIRCULAR MEMBER AND THE DIAMETER OF THE UNDISTORTED LOOP BEING GREATER THAN THE RADIAL SEPARATION BETWEEN SAID RING AND SAID CIRCULAR MEMBER SO THAT WHEN SO DISTORTED THERE IS AN APPRECIABLE ARC OF CONTACT BETWEEN SAID SPRING AND EACH OF SAID RING AND SAID CIRCULAR CONTACT MEMBER. 